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HK: Fachverband Physik der Hadronen und Kerne

HK 6: Heavy-Ion Collisions and QCD Phases II

HK 6.4: Vortrag

Montag, 20. März 2023, 17:30–17:45, SCH/A315

Real-time methods for spectral functions — Johannes Roth¹, •Leon Sieke¹, and Lorenz von Smekal^1,2 — ¹Institut für Theoretische Physik, Justus-Liebig-Universität, 35392 Giessen, Germany — ²Helmholtz Research Academy Hesse for FAIR (HFHF), Campus Giessen, 35392 Giessen, Germany

We compare different real-time methods to calculate spectral functions in dissipative open systems based on generalized Langevin equations. These are classical-statistical lattice simulations, a quasiclassical approximation and a Gaussian state approximation (GSA) which is the main focus of this talk. Results from exact diagonalization of the quartic anharmonic oscillator with damping serve as benchmark which can be seen as a (0+1)-dimensional toy theory for self-interacting scalar fields at finite temperature. Inspired by the well-known Caldeira-Leggett model, we extend the classical Langevin dynamics for the coupling to an external heat bath to the corresponding Heisenberg-Langevin dynamics in the GSA [1]. We furthermore use the latter to compute spectral functions in a self-interacting scalar field theory in (2+1) and (3+1) dimensional spacetime. To achieve this we employ two different methods to compute the spectral functions which work particularly well in complementary temperature regimes.

[1] J. V. Roth, D. Schweitzer, L. J. Sieke and L. von Smekal,
Phys. Rev. D 105 (2022) 116017.